The machines covered by this requirement are intended for use in the aircraft manufacturing industry, and provide the preferred relation of spindle horse power, speeds and feeds for the simultaneous turning of each side of jet engins compressor and turbine rotor discs, or other parts of a similar configuration, where oil canning is a hazard in the turning operation in relation to finished part requirements.

These discs are mostly forgings of aluminum, of stainless steel, titanium and other hi-heat alloys non commonly used in aircraft manufacture.